The present invention relates to vehicles and is directed towards a method for preventing, in a gearbox coacting with a system for automatic gear selection, the selection of an operationally incorrect gear in the cases where the r.p.m. of a vehicle wheel is not a correct representation of the vehicle speed, e.g. during braking of the vehicle, means in the system calculating the instantaneous r.p.m. alteration of the wheel, comparing it with a predetermined retardation value and sending an output signal if the calculated r.p.m. variation exceeds said predetermined retardation value, said output signal activating an operative circuit or the like which thereby caters for the selection of a neutral gear position and/or triggers fault indication in alarm means.
Through the U.S. Pat. No. 4,126,061 it is previously known to make a retardation comparison when a vehicle is braked and to let the output signal from such a comparison control the energization of an operative circuit which causes selection of a neutral gear position for a predetermined period of time, after which the system returns to a normal condition. The means that the known system mentioned returns after a longer braking process, especially a pulsing process, to normal gear selection in spite of braking still being in progress. Unsuitable gear selection will be the result hereof, which can have fatal consequences when the selected gear is engaged, from the aspect of mechanical as well as traffic safety.